1. Field of the Invention
This invention relates to a semiconductor device and manufacturing method thereof for providing a stable connection between an impurity diffusion region formed in a semiconductor substrate and a wiring layer formed on the surface of an insulation film on the semiconductor substrate via a contact hole formed in the insulation film.
2. Description of the Related Art
In a semiconductor device, generally, oxide film regions are selectively formed on the surface of a semiconductor substrate for separating devices from one another along the surface of the substrate. At least one impurity diffusion region is formed in the semiconductor substrate between such oxide film regions. An insulation film is then formed on the semiconductor substrate, and a wiring layer is formed on this insulation film. The impurity diffusion region and wiring layer are connected together by way of a contact hole formed in the insulation film.
When the width of the contact hole is greater than the width of the impurity diffusion region, a portion of the contact hole extends to the oxide film which is adjacent to the impurity diffusion region. As a result, the wiring material formed in the contact hole directly contacts the semiconductor substrate, causing a so-called current leak. To avoid this problem, the width of the contact hole is usually set to be smaller than the width of the impurity diffusion region. Additionally, the forming position of the contact hole is set at a position remote from the oxide films.
Meanwhile, an integration of the semiconductor integrated circuit increases and the semiconductor elements become smaller, the device areas defined by the oxide films becomes smaller, and the area of the impurity diffusion regions formed therein also tend to be smaller. As a result, the width of the contact hole is becoming smaller.
When the area of the contact hole becomes smaller, the contact resistance between the impurity diffusion region and wiring layer increases. Additionally, the smaller the area of the impurity diffusion region, the shorter the distance between the periphery of the contact hole and the edge of the oxide film. As a consequence, the patterning allowance between the impurity diffusion region and the contact hole decreases, and positioning of the two becomes extremely difficult.